1. Field of the Invention
This invention relates to a fuel injection pump for diesel engines comprising a housing which contains a pump cylinder sleeve that has at least one radial fuel port and a plunger that is slidably mounted in the cylinder sleeve and has two axially spaced apart valving edges, which cooperate with the fuel port, and a cylindrical plunger follower, which is movably mounted in the housing and coupled to the plunger and is moved against the force of a return spring by an actuating member which is driven by a camshaft, wherein the stroke position of the plunger is adjustable by means of a stop, which is adjustable by means of a timing piston, which is disposed in a timing cylinder and is adapted to be supplied with oil under pressure through a check value and is adjustable to a limited extent, and wherein an oil passage leads into the plunger follower.
2. Description of the Prior Art
A change of the stroke position of the plunger or a change of the initial position of the valving edges of the plunger relative to the fuel port in the cylinder sleeve will result in a change of the timing of the beginning of the discharge by the fuel injection pump and of the injection of fuel into the combustion chanber of the diesel engine. A decrease of the distance existing between the valving edge which determines the beginning of the discharge stroke and the fuel port when the plunger is in the corresponding dead center position will have the result that the stroke position of the plunger is shifted toward said port and the valve edge will sooner arrive at the fuel port so that the discharge will begin sooner after the fuel port has been closed. The discharge of fuel will begin later when the distance is increased that exists between the valving edge and the fuel port when the piston is in its dead center position assumed at the beginning of the discharge stroke.
A fuel injection pump of the kind described first thereinbefore is known from U.S. Pat. No. 3,859,973. In that pump the actuating member which acts against the plunger follower against the force of the return spring is operated by the camshaft via a rocker lever, which at its end that is adjacent to the pump contains an inserted cylinder sleeve which has a cylinder opening in which the timing piston is accommodated. The stroke of the timing piston is limited by a crosspin, which extends through the timing piston in a bore with a relatively large radial clearance. The rocker lever contains bores for conducting hydraulic oil which is supplied under pressure and which open into the cylinder opening through a disc check valve. The return spring for the plunger cooperates with an abutment, which is not rigid with the plunger follower but is connected to the latter by a weaker spring, which serves as a return spring for the timing piston. The actuating member is interposed between the free end face of the plunger follower and the timing piston so that the latter serves as a stop which determines the stroke position of the plunger and of the plunger follower. The coupling between the plunger and the plunger follower has virtually no backlash in the axial direction and the cylinder sleeve which contains the timing piston has no controlled oil outlet port. The oil passage which extends through the actuating member into the plunger follower is merely a passage for supplying lubricating oil to the sliding surfaces of the plunger flower and the housing. That arrangement has the disadvantage that the cylinder sleeve which contains the timing piston and the check valve are disposed in the end portion of the rocker arm. That arrangement involves a considerable structural expenditure and requires the rocker arm to have large dimensions so that its accommodation may be difficult. A particularly significant fact resides in that when the timing piston has been supplied with hydraulic oil in a sense to advance the beginning of the discharge from the fuel injection pump the timing piston can return only slowly to its initial position because a controlled outlet opening for the hydraulic oil is not provided and the hydraulic oil can only leak out between the cylinder sleeve and the timing piston. As a result, the adjusting speed is relatively low. Higher adjusting speeds could only be achieved if a higher leakage was tolerated but this would result in an appreciable loss of hydraulic oil from the working space in the cylinder sleeve during the discharge stroke. Such a loss of oil would result in a generally undesired increase of the duration of the injection of fuel. Owing to the time required by the oil to leak out of the timing cylinder, the frequency of the fuel injection pump is limited during the discharge stroke.